Birth control pills have been the leading method for preventing pregnancy in the United States since they were approved by the U.S. Food & Drug Administration (FDA) in 1960. They’re effective, readily accessible, and inexpensive.

Birth control pills are generally considered safe for most women. While they do have some risks, newer low-dose birth control pills can reduce those risks.

Most birth control pills today are considered low-dose. This includes both combination pills (estrogen and progestin) and the minipill (progestin only).

Low-dose pills contain 10 to 30 micrograms (mcg) of the hormone estrogen. Pills that only have 10 mcg of estrogen are classified as ultra-low-dose. Estrogen is in most birth control pills, and it’s linked to an increased risk of health problems, such as blood clots and stroke.

The exception is the minipill. It’s available in only one dose that contains 35 mcg of progestin.

Birth control pills that aren’t low dose may contain up to 50 or so mcg of estrogen. These are rarely used today, as lower doses are available. By comparison, the first pill to enter the market contained 150 mcg of estrogen.

The hormones estrogen and progesterone signal your body to produce eggs and prepare for pregnancy.

If a sperm doesn’t fertilize the egg, the levels of these hormones fall steeply. In response, your uterus sheds the lining that had built up. This lining is shed during your period.

Birth control pills contain either a combination of synthetic estrogen and synthetic progesterone or synthetic progesterone alone. This manmade version of progesterone is also known as progestin.

Estrogen and progestin work in different ways to prevent pregnancy. Both work to prevent the pituitary gland from producing hormones that trigger ovulation.

Progestin also thickens your cervical mucus, making it harder for sperm to reach any released eggs. Progestin thins the uterine lining as well. This makes it harder for an egg to implant there if the sperm fertilizes it.

Combination birth control pills contain estrogen and progestin. When they’re taken correctly, combination birth control pills are 99.7 percent effective in preventing unwanted pregnancy. With typical use, such as missing a few doses, the failure rate is about 7 percent.

Progestin-only pills may be a good option if you have risk factors that prevent you from taking estrogen, such as smoking or a history of heart disease.

There are other advantages of low-dose progestin-only pills:

You can take them if you’re breastfeeding.

They reduce your risk of endometrial cancer or PID.

You may have fewer periods.

You may experience less cramping.

The disadvantages of low-dose progestin-only pills can include:

spotting between periods

periods that are more irregular

Other side effects include:

bloating

weight gain

sore breasts

headaches

depression

ovarian cysts

Pain, the pill, and sex A study of nearly 1,000 women at New York University Langone Medical Center found that women taking low-dose birth control pills were more likely to experience pain and discomfort during sex than women taking standard birth control pills.

The progestin-only pill is often called a “minipill.” This type of birth control is also 99.7 percent effective when taken correctly. The typical failure rate is about 7 percent.

If you miss a dose or don’t take the minipill at the same time each day, your chance of becoming pregnant is greater than it would be if you used low-dose combination pills. When minipills aren’t taken correctly, their effectiveness becomes even lower.

Although minipills can produce side effects, particularly bleeding or spotting between periods, the side effects often improve or disappear after a few months. The minipills can also shorten the length of your period.